The clear path for future color CRT development is in the direction of high definition television (HDTV) displays. This is true whether operating in accordance with the NTSC standard or the PAL format. Regardless of the color television system, a HDTV display requires a higher frequency magnetic deflection yoke and high video image resolution and brightness. Increased display performance does not come without a price.
Increasing the scan frequency of the CRT's magnetic deflection yoke requires higher deflection input power to the yoke as well as a more expensive yoke assembly. To provide acceptable brightness and resolution in a large 16:9 color CRT, higher beam current and improved video image resolution are required. These enhancements typically require a larger CRT envelope neck size to accommodate a larger electron gun. Increasing the size of the CRT envelope is contrary to current trends which seek to reduce the non-display screen portions of the CRT. One approach to providing acceptable image brightness involving the use of higher beam currents employs a dispenser cathode which affords high electron emission densities. However, the use of a dispenser cathode substantially increases the cost of the cathode, i.e., on the order of 50 times more than that of a conventional oxide cathode, to the point where these exotic cathodes are at present not commercially viable for use in a CRT. While some of the aforementioned approaches have been adopted in high definition television (HDTV) CRT's, the increased cost and complexity of the resulting CRT reduces its commercial competitiveness relative to other HDTV display technologies such as liquid crystal displays (LCDs), plasma display panels (PDPs), etc.
Referring to FIG. 1, there is shown an isometric view partially in phantom of a typical prior art multi-beam electron gun 10 for use in a color CRT. A sectional view of the electron gun 10 shown in FIG. 1 taken along site line 2--2 therein is shown in FIG. 2. Electron gun 10 includes a plurality of spaced, inline cathodes 12, 14 and 16 which each provide respective pluralities of energetic electrons in the general direction of a G1 control grid 18 having a plurality of spaced, inline apertures 18a, 18b and 18c. The energetic electrons are directed through apertures 18a, 18b and 18c and toward a G2 screen grid 20 having a corresponding array of inline apertures 20a, 20b and 20c. The G1 control grid 18 and the G2 screen grid 20 comprise a beam forming region (BFR) 46 for forming the pluralities of energetic electrons into three inline electron beams 22, 24 and 26 shown in dotted-line form. Electron gun 10 further includes a G3 grid 28 and a G4 grid 36 aligned along the electron gun' s longitudinal axis. The G3 grid 28 typically includes a plurality of inline apertures 28a, 28b and 28c in facing relation to the G2 screen grid 20 as well as an inner metal plate 32 containing a plurality of inner inline apertures 30a, 30b and 30c. The G3 grid further includes a horizontally aligned, elongated chain link-shaped common aperture 34 in facing relation to the G4 grid 36. The G4 grid 36 similarly includes a horizontally aligned, elongated chain link-shaped common aperture 39 in facing relation with the G3 grid 28. The G4 grid 36 further includes an inner metal plate 38 containing three inline apertures 36a, 36b and 36c which respectively pass electron beams 22, 24 and 26. The combination of the G3 grid 28 and the G4 grid 36 form a high voltage focus lens 48 for accelerating and focusing the three electron beams 22, 24 and 26 on the display screen, or faceplate, 40 of the CRT. Disposed on the inner surface of display screen 40 is a phosphor layer 52 which emits light in response to the electron beams incident thereon. The G1 and G2 grids 18, 20 are respectively coupled to and charged by V.sub.G1 and V.sub.G2 voltage sources 41 and 43. The G3 and G4 grids 28, 36 are respectively coupled to and charged by focus (V.sub.F) and accelerating (V.sub.A) voltage sources 45 and 47.
An elevation view of the CRT's display screen 40 is shown in FIG. 3 which also illustrates the horizontal scan lines 42 over which the electron beams are displaced by means of the CRT's magnetic deflection yoke (not shown for simplicity) in tracing out a video image on the display screen. For simplicity, only 12 scan lines are shown in the figure, it being understood that there are many more horizontal scan lines in the typical CRT. The beginning of electron beam trace for the first horizontal scan line is shown by the arrow in the upper left-hand corner of FIG. 3, while the beginning of electron beam trace of the last horizontal scan line is shown by the arrow in dotted-line form in the lower left-hand corner of the figure. The electron beams are converged in the form of a spot 44 on the display screen 40 which is traced across the display screen in a raster-like manner in proceeding from left to right and from top to bottom as viewed in FIG. 3. Each horizontal sweep of the electron beams of faceplate 40 provides a single horizontal line of the video image displayed thereon. Electron gun 10 is typical of those used in conventional inline color CRTs which generally suffer from the design and operating limitations discussed above.
The present invention addresses the aforementioned limitations of the prior art by providing a multi-beam group (MBG) electron gun for use in a color CRT wherein two or more vertically spaced, horizontal inline electron beam arrays provide the primary colors of red, green and blue to adjacent horizontal scan lines on the CRT display screen permitting two or more adjacent lines of the video image to be simultaneously formed on the display screen.